I think your calculation leaves out any consideration of natural climate variability (very common among climatologists). If you want to “empirically test these model fits” I would suggest you take changing temperature trends into account. From 1945 to 1975, CO2 was rising yet temperature was falling. This has to tell us something important (even if it is only to help us calculate the level of natural climate variability).

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By: DAV https://climateaudit.org/2008/01/10/the-ipcc-simplified-expressions/#comment-131500
Sat, 12 Jan 2008 08:16:35 +0000http://www.climateaudit.org/?p=2586#comment-131500Rats! I accidentally hit CR while spell checking that post. Caused it to be submitted before I was through (*sigh*)
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By: DAV https://climateaudit.org/2008/01/10/the-ipcc-simplified-expressions/#comment-131499
Sat, 12 Jan 2008 08:13:58 +0000http://www.climateaudit.org/?p=2586#comment-131499I guess I really should explain why I see the different curve equations for different gases a problem. Along the way, I may cast some light on Steve’s logarithm question.

All I can say is if you are insisting on looking at the bandpass characteristics of a gas you are not only missing the forest for the trees but you don’t even see the trees because of all of the darn twigs that are in the way. Temperature in regard to climate is a macro effect. It’s an average of many complex kinetic interactions. The equations that I was referring to are using atmospheric concentrations (in ppm) to arrive at some additive temperature rise.

Just an overall expectation: for any given gas, I think you should be able to come up with a pretty simple formula. GHG’s are going to raise temperature in pretty much the same manner as building insulation. That is, they impede the flow of energy. Steve made a comment that electrical equations are just an analogy but the reality is that electrical circuits are an analogy only in the sense that thermodynamic analyses and electrical analyses are dealing with different forms of energy transfer. In many, if not all, respects they are equivalent. Thermal resistance is used in the same manner in thermo in the same manner as resistors are used in electrical engineering.

The bandpass characteristics of a gas are nice to know. For one, it explains why GHG effect is largely a one way effect. I would think that the energy coming from the Sun has a fixed energy distribution with regard to frequency. Likewise for the Earth’s radiation back into space. So given that distibution, the antenuation provided by a gas should be pretty much fixed. When you talk about increasing the concentration of gas, you are just talking about more of the same thing. So, on the surface, you’d think it would be a fairly straightforward equation.

The form would be expected to be logarithmic. In building insulation, every bit you add has a diminishing return. 100 cm of insulation isn’t much better that 99 cm percentagewise. The reason is that in the outer layers, there is less energy flow to impede.

Now, gasses aren’t quite that simple. First, in low concetrations, they tend to spread out. But in the climate world that’s pretty much already taken care of in the statement of concentration. Secondly, bulding insulation is pretty much fixed in position. Gasses, however, are free to move about and will change altitude depending upon how much heat they’ve absorbed. This may have a noticeable effect but I’m not sure how.

Okay, then, I acknowledge that the total antenuation based upon concentration might not be a simple expression. But I still think one gas is pretty much interchageable with any other. A given gas may have some thermal resistance, X, at some unit concentration and another may have Y. But that doesn’t explain the different gasses have such a wild difference in form as the ones given for CO2 and methane. I’d think both would be of the form R(gas)A(conc), where R(gas) gives the gas’s thermal resistance (I would expect this to be a fixed value as it is for other insulators) and A(conc) gives the gaseous attenuation response for a give concentration. I would expect that to be the same for all gasses. The only exception that I can see is how the gas may rise when heated.

So, maybe that’s why the equations are so different? Or maybe they just look different?

In a previous post that has been shooed off to elsewhere, I made the unwarranted assumtion that doubling the concentration leads to doubling the thermal resistance. That would only be close to true in very low concentrations. The change in resistance is what is logarithmic. If you are working bacwards from power/unit area (watts/m^2), that too is logarithmic.

I confess I haven’t read all pf the papaers yet. I need to do this. Still, those equations are bothering me.